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Abstract

The O+ 4 radical cation has been generated by two different methods and trapped as an isolated ion in neon matrices at 4 K for electron-€spin resonance (ESR) investigation. The O+ 4 species is a potentially important atmospheric ion for which little experimental or theoreticalinformation is available. These ESR results indicate that the electronic ground state of O+ 4 is a nonlinear quartet (S=3/2) with the three unpaired electrons occupying primarily 2p(Ï€) orbitals. The fine structure-€parameters obtained from an analysis of the ESR spectrum are D=1.875(5) and E=0.0350(5) cm-ˆ’1 . The isotopic ions1 6 , 1 7 O+ 4 were also generated but the 17 O hfs could not be fully analyzed because of the large number of overlapping hyperfine lines.